Method of fabricating heat exchangers



Patented July 11, 1950 uNrEo -s'rii'ras PATENT l orales 'rh E. Bureau-ae Dumm, o an@ in glacial Motors Corporation, mi?, a corporation of Delaware Application October 31, 1947, Serial No. '183,400 c claims. im 11a-nal" This invention relates to refrigeration and particularly to closed heat exchanger elements employed in refrigeratng systems.

An object of my invention is to provide a sheet metal heat exchanger for use in refrigeratlng systems that will be of improved appearance, more eiiicient and of lower manufacturing oost.

Another object oi' my invention is to provide an inexpensive successful method of fabricating a sheet metal heat exchanger from aluminum and/or aluminum alloy sheets whereby the use thereof in a refrigerating system is rendered practical.

A ftherand more speciiic object of my invention is to provide a method of fabricating an evaporator for a refrigerating system from metal sheets, one of which is provided with a continuous corrugation to form, when the sheets are heated and bonded together, a series iiow passageway between the sheets and to prevent selected or predetermined points of the sheets from being secured to one another, while certain other portions of the sheets are being bonded together, whereby the unsecured or unbonded portions of one of the sheets maybe deformed or expanded to provide conduitsinterconnecting runs of the continuous corrugation in the other sheet and thereby divide the series iiow passageway into a plurality of parallel iiow4 passageways.

Further objects and advantages of the invention will be apparent from the following description, reference being had to the accompanying drawing wherein an article fabricated in accordance with the present method is illustrated;

In the drawings:

Fig. 1 discloses a metal sheet having a continuous corrugation formed therein superimposed upon a flat metal sheet with a bonding material therebetween and showing inserts at predetermined points between the sheets.

Fig. 2 is an enlarged fragmentary sectional view taken on the line 2-2 of Fig. 1 showing the superimposed plate-like structure with a bonding shim and one of the inserts between the metal sheets.

Fig. 3 is a view similar to Fig. 2 showing the elements of the double walled plate-like structure after being bonded together.

Fig. 4 is a, fragmentary sectional view of the bonded structure showing confinement thereof prior to the application of pressure internally of the double walled structure. A

Fig. 5 is aview similar to Fig. 4 and shows the deformation of a part of one wall of the bonded together double walled structure.

Fig. 6 discloses the bonded together double walled structure with the deformed parts of one wall thereof forming conduit connections across iruns of the series or continuous oorrugation; Fig. I is a fragmentary view' showing the bonded together structure disclosed in Fig. 6 bent or folded into a Substantially Ueshaped heat exchanger.

For the purpose of illustrating my invention,

llwilldcribethemanufaatln'eofaclosedor fluid type heat er such, for example, as an evaporator or cooling element for use in refrigeratingsystems. ReferringtoFigiofthe drawing, I have shown a substantially fiat platelike unit i@ superimposed metal sheet portions il and i2 (see Hg. 2),. The sheet portions ii and i2 may be two separate metal sheets or the miperimposed unit It may be formed by bendingorfoldingapartofasinglemetalsheet over and upon another part of the same sheet.

25 or rolled, in any suitable and well-known The edge of one of the metal sheets may, if desired, be folded over the edge portions of the other metal sheet to better seal the unit lil. A continuous eorrugaizion or tion is stamped in one of the sheet metal portions i2 and extends in spaced apart adiaeent runs or convolutions M throughout the length of unit iii.

The return bends of alternate runs or convolutions may be larger in radius than other of the retm'nbendsasinditedat iSinFg. 1 soas to position the return bends ofthenms i4 closer to one another for facilitating the out of the proeess to be hereinafter described. The continuons eoi'rugation provided in the one sheet metal pm'tion i2 forms, when this sheet portion is superimposed upon sheet portion li, a series dow passageway i5 (see Fig. 2) between the sheet portions il :and i2 andthisewayhas an inlet opening i8 and an outlet opening i9 located at the longer edges of the unit l0 (see Fig. i).

A bon material, indicated at 3i in Eig, 2 of the is located between the superimposed sheet metal portions i i and i2. This bonding material may be bmshed on the adjacent surfaces of the sheets il and i2 or the bonding materialanaybeintheformoashimorfoil placed between the sheet metal portions ii and i2. In the present method it is desirable to prevent bonding of all portions of the adjacent surfaces of 'the sheet portions li and i2 and various ways of avoiding bonding of selected or predetermined poin or parts of the adjacent surfaces of the sheet portions may be employed while the unit iisheatedtomeltthe bondingmaterial and cause bonding of the sheet portions II and I2 together. In order to carry out the preventing` of bonding of selected points of adjacent surfaces of the sheet portions II and I2 such points on the surfaces of the sheets may be plated or coated with any desired or suitable substance to render them incapable of being secured together by the bonding material employed. For example, these points may first be plated with copper or zinc and thereafter covered or coated with chromium by plating the chromium over the copper or zinc. However, in the present disclosure I cause these selected points,'between the sheets II and I2, to remain unbonded during heating of the unit I by providing a block or restriction to the flow of the bonding material over the selected adjacent surfaces. These blocks may be in the form of discs or square or rectangular washers 23, as herein illustrated, placed between the sheet portions II and I2 (see Fig. 2) at the selected points indicated by the dotted line showing of the washers 23 in Fig. 1. While I have shown the washers 23 as being located at the return bends I5 of the runs I4 of the continuous corrugation, it is to be understood that they may be positioned at any desired points along the runs I4'. The washers or inserts 23 may be secured in the desired locations or selected points in any suitable manner such as being spot welded to the one sheet II or by staking some of the material of the metal sheet portion II into the opening in washers 23 as indicated by the reference character 24 in Fig. 2 of the drawing. In the case of utilizing the bonding material 2l in shim or foil form, the shim 2I will preferably be cut out or provided with holes for straddling the washers 23. The bonding shim or bonding material 2| may have a suitable flux admixed therewith or incorporated therein or the fluxing material may be brushed on or plated upon the surfaces to be bonded together as is common practice in the brazing art.

After the unit IIl is assembled in the manner aforesaid it may be placed in or passed through a suitable or conventional furnace, such as is fully described in the S. M. Schweller Patent No. 2,067,208 or in the C. A. Mann Patent No. 2,093,814 and bodily heated to a temperature sufcient to cause melting of the bonding shim 2l, in the presence of the fluxing material by radiant heat. In this manner uniform heating and bonding together of all adjacent surface portions of the sheets II and I2 is obtained except at the selected points of location of the washers 23. The bonding material will not ow over or upon a chrome plated surface and will not stick or bond thereto, thus the washers or inserts 23 are preferably -plated with chromium. The -washers 23 may be tightly pressed between adjacent surfaces of the sheet metal portions II and I2 by weights or any other suitable means during heating of unit I0 to effectively prevent flow of the fused bonding material 2l over the flat selected surfaces of sheet portions II and I2 contacted by the washers and consequently these selected surfaces or points remain or will be left unbonded or unsecured together while other adjacent surfaces thereof are bonded. Bonding of the sheet portions II and I2 together in the manner described provides an integral structure IIIa (see Fig. 3), having the closed series ow passageway I6 formed therein. After the structure I0a has cooled, suitable fittings II (see Fig. 6) may be hand brazed in the inlet and outlet 4 openings I8 and I3 respectively ofthe passageway I6. These ttings II permit the connection of the passageway I6 with a suitable pumping apparatus which pumps a cleaning or solvent solution, under pressure, through the series flow passageway I6 to dissolve and remove from the passageway any residue of the flux which may have deposited therein during bonding of the sheet portions Il and I2 together. The cleaning solution is provided with a positive path of flow through sturcture I0a and since there are no traps or pockets in the series flow passageway I6 which are not contacted by the solution, a thorough cleansingof this passageway is insured. The structure Ilia, after having the series flow passageway I6 extending therethrough thoroughly cleaned out, is placed in a suitable mold or holding tooly represented by the reference character 3I (see Fig. 4). The tool 3| is provided with wall portions 32 clamping and conning the bonded together parts of the structure Ia in place. Tool 3l is also provided with wall portions 33 extending across the unbonded portions or selected points at which the washers f 23 are located. The one part 34 ofthe holding tool 3l is provided with a bleeder opening 3E extending from the wall 33 to the atmosphere outside the tool for a purpose to be presently described. One one of the series flow passageway is plugged and a suitable or conventional hydraulic or other pressure creating device (not shown) is connected to the other end of the series flow passageway I6. This device establishes a sufficiently high pressure internally of the passageway I6 of structure Illa to cause the wall y parts of sheet portion I2, indicated at 38 in Figs. 4 and 5 ofthe drawing, at the unbonded selected points to be forced or deformed outwardly away from the sheet portion II against the wall portions 33 of the tool 3| as shown in Fig. 5. The deformation of the wall 38 provides passages, indicated by the double-headed arrow 39 in Fig. 5, interconnecting the passageways I6 of adjacent runs I4 of the continuous corrugation and these interconnecting passages 39 maybe formed at any point or at a plurality of points along the length of the corrugated runs I4. For example, washers 23 may be located along the straight runs or ducts I4 intermediate the return bends I5 to provide interconnecting passageways as shown at 21 in Fig. 6. Such intermediate 'passageways 21 would be disposed along the bottom wall of the evaporator illustrated in Fig. 7 of the drawing to thereby divide the parallelly connected passageways into a plurality of shorter parallel flow passageways. Any air entrapped under the wall portions 33 of tool 3I, during the application of pressure internally of structure IIia, will escape through the hole 36 to permit the Wall parts 3B to be corrugated or forced outwardly of the washers 23 and against the wall portions 33 of the tool. This deformation or corrugation of the wall parts 38 of structure I0a' occurs at the selected points 4of llocation of the washers 23 shown in dotted lines in Fig. 1 of the drawing and transforms or changes the' series flow passageway I6, extending through the structure Illa, into a plurality of parallelly connected or communicating passageways between the inlet I I8 and the outlet I9`of the sheet metal structure as clearly illustrated in Fig. 6. During and after deformation of the wall parts 38 of thebonded structure Ilia, as described, washers 23 will remain secu-red to the sheet portion II of the structure due to the staking of metal of the sheet II into the central opening of the washers and consequently these washers will not interfere with flow of refrigerant in or through the plurality of parallelly connected passageways. The bonded structure Ina shown in Fig. 6 of the drawing may be bent or rolled into any desired shape such, for example, as into a substantially U- shape, as shown in Fig. 7, which is common practice to form an evaporator for household refrigerating cabinets and which U-shaped evaporator provides walls of a sharp freezing chamber, for the reception of trays of water or other substance to be frozen by the refrigerating effect produced by the evaporator. In the form of evaporator shown in Fig. 7 of the drawing the pressure formed corrugations 38 connecting the return bends i5 of the runs I4 of the passageway I6 provide a header at the upper end of each leg of the U-shaped evaporator for the free and unrestricted circulation of refrigerant through the plurality of parallelly connected passageways. After forming the structure into the U- shape illustrated, or into any other desired shape, the appearance of the exterior walls of the evaporator may be enhanced by coating or plating the surfaces thereof in any well known or conventional manner.

While the method herein disclosed may be employed to fabricate evaporators or condensers from various sheet materials, it is especially adaptable to the fabrication of such elements from aluminum or aluminum alloy sheets, whereas such fabricating has heretofore been impractical. In an evaporator wherein the ow of refrigerant is desired through a, plurality of parallelly connected passageways, ordinarily preformed in one of the sheets from which the evaporator is fabricated, such passageways could not be properly cleaned out after the bonding operation and ilux residue or deposits remaining in the passageways would, upon charging refrigerant into the evaporator, or into the refrigerating system, form with the deposits certain acid compositions or the ike. These acids corroded the aluminum sheets and would cause their decomposition in short time. In practicing my improved method thorough cleansing of flux residue from the interior of the evaporator is, by virtue of the preformed series ow passageway, insured and which passageway is thereafter deformed to provide the desired number of parallelly connected passageways. The present method therefore permits the utilization of relatively inexpensive rolled sheets of aluminum or aluminum alloy in the fabrication of heat exchangers. This material is more desirable than certain other materials, due to its good heat conducting properties and its non-'corrosive properties. A neat appearing and lasting finish can be provided on the exterior surfaces of heat exchangers fabricated from aluminum sheets. I may employ aluminum sheets ranging from substantially pure aluminum to aluminum alloy sheets having a chemical composition of .2 to .12% copper, 0 to .5% iron, 0 to .7% silicon, 0 to 1.25% manganese, 0 to .5% zinc, 0 'to .35% chromium, 0 to 2.8% magnesium and the remainder pure alumium. Any aluminum sheet composition Within the limits specied may be effectively and practically anodized with any. of the presently known anodizing apparatuses or processes. Therefore, I anodize the exterior surfaces of the evaporator shown in Fig. 7 of the drawing so as to provide these surfaces with a uniform bright appearance. In the use of aluminum sheets the discs or washers 23 are preferably made of steel material and chrome plated so as not to be affected by the refrigerant in the evaporator whereby these washers will not cause corrosion or deterioration within a refrigerating system. In order to bond the desired portions of the sheets together by a, process involving radiantly heating the entire exposed surfaces of the superimposed aluminum sheets I may employ an aluminum bonding or brazing alloy having the chemical composition of approximately 2.3 to 5% copper, 0.8% iron, 1 to 10% silicon, .15% manganese. .20% zinc, .15% chromium, .15% magnesium and the remainder pure aluminum. It should be understood that these ingredients of the brazing or bonding material may be varied in accordance with the chemical composition of aluminum sheets to be bonded together. One example of a ux suitable for causing bonding of the aluminum sheets together with the bonding material specified may be a compound consisting of eighteen parts lithium chloride, ten parts zinc chloride, four parts stearic acid, thirty parts potassium chloride and eight parts aluminum acetate. Another flux suitable for causing bonding of the aluminum sheets together and which may be in liquid or paste form and when dry has a composition of approximately 32% sodium chloride, 24% potassium chloride, 24% lithium chloride and 20% sodium fluoride. It is also to be understood that the ingredients of the iluxing compound may be varied in accordance with variations in the composition of both the aluminum sheets and the bonding or brazing alloys employed.

In view of the foregoing the objects of my invention become obvious in that I provide a method of fabricating fiat aluminum or aluminum alloy sheets into evaporators and/or condensers for use in refrigerating systems, as distinguished from cast or extruded aluminum to greatly reduce manufacturing costs of such heat exchangers.

I claim:

1. The method of making a closed heat exchanger for a refrigerating system which consists in, forming a continuous corrugation having a plurality of spaced arpart runs connected in series by return bends in a sheet metal portion and superimposing the corrugated sheet portion upon another sheet metal portion with a bonding material therebetween whereby the corrugation initially provides a, series flow passageway between the sheet portions, uniformly applying heat simultaneously over the entire exposed surfaces of the superimposed sheet portions to melt the bonding material and bond surfaces of the sheet metal portions around said continuous corrugation together, preventing surfaces of said sheet metal portions at selected localities intermediate said return bends and extending between certain adjacent spaced apart runs of said series flow passageway from being bondedtogether, directing a cleaning fluid through said series flow passageway to remove foreign matter from the interior of the exchanger while preventing fluid iiow between said certain runs at said selected localities, and thereafter applying pressure internally of said passageway to expand one of said sheet metal portions at said unbonded selected localities whereby said series flow passageway is divided into a plurality of parallel ilow passageways.

2. The method of making a closed heat exchanger for a refrigerating system which consists in. forming a continuous corrugation having a plurality of spaced apart runs connected in series by return bends in a sheet metal portion and superimposing the corrugated sheet portion upon another sheet metal portion with a bonding material therebetween whereby the corrugation initially provides a series flow passageway between the sheet portions. uniformly applying heat simultaneously over the entire exposed surfaces of the superimposed sheet portions to melt the bonding material and bond surfaces of the sheet metal portions around said continuous corrugation together, preventing surfaces of said sheet metal portions at selected localities extending between adjacent return bends of said series flow passageway from being bonded together, directing a cleaning fluid through said series flow passageway to remove foreign matter from the interior of the exchanger while preventing fluid now between adjacent return bends at said selected localities, and thereafter confining the bonded together surfaces of the sheet metal portions and applying pressure internally of said passageway to expand one of said sheet metal portions at said unbonded selected localities to provide a header communicating with said return bends.

3. The method of making a closed heat exchanger which consists in, forming a continuous corrugation having a plurality of spaced apart runs connected in series by return bends in an aluminum sheet portion and superimposing the corrugated aluminum sheet portion upon another. aluminum sheet portion lwith a bonding material therebetween whereby, the corrugation initially provides a series ow passageway between the sheet portions. uniformly applying heat simultaneously over the entire exposed surfaces of the superimposed aluminum sheet portionsto melt the bonding material and bond surgether, directing a cleaning nuid through said series i'low passageway to remove foreign matter from the interior of the exchanger while preventing fluid flow between adjacent return-bends at said selected localities, and thereafter connning the bonded together surfaces of the aluminum sheet portions and applying pressure internally of said passageway to expand one of said aluminum sheet portions at said unbonded selected localities to provide a header communicating with said return bends.

5. The method of making a closed heat exchanger which consists in, forming a continuous corrugation having a plurality of spaced apart runs connected in series by return bends in a sheet metal portion and superimposing the corrugated sheet portion upon another sheet metal portion with a bonding material therebetween and with inserts of a material that will not bond to said sheet metal portions or to said bonding material between and in contact with the sheet portions and extending frrm one of said runs to an adjacent run of said corrugation intermediate said return bends, securing said inserts to between the sheet metal portions. directing a faces of the sheet portions around said contlnuous corrugation together, preventing surfaces of said aluminum sheet portions at selected locallties intermediate said return bends and extending between certain adjacent spaced apart runs of said series flow passageway from being bonded together, directing a cleaning uid through said series flow passageway to remove foreign matter from the interior of the exchanger while preventing fluid flow between said certain runs at `said selected localities, and thereafter applying pressure internally of said passageway to expand one of said aluminum sheet portions at said. un bonded selected localities whereby said series flow passageway is ,divided into a plurality of parallel ow passageways.

4. The method of making a closed heat exchanger which consists in, forming a continuous corrugation having a plurality of spaced apart runs connected in series by return bends'in an aluminum sheet portion and superimposing the corrugated aluminum sheet portion upon another aluminum sheetportion with a bonding material therebetween whereby the corrugation initially provides a series flow passageway between the sheet portions, uniformly applying heat simultaneously over the entire exposed surfaces of the superimposed aluminum sheet portions to melt the bonding material and bond surfaces of the sheet portions around said continuous corruchanger which consists in, forming a continuous cleaning fiuidfthrough said open series flow passageway to remove foreigmmatter from the interior of the exchanger while preventing uid flow from said one run to said adjacent run at the point of location of said inserts, and thereafter applying pressure internally of said passageway to expand the unbonded portions of one of the sheet portions at said inserts whereby said series flow passageway is divided into a plurality of parallel flow pusageways.

6. The method of making a closed heat excorrugation having a plurality of spaced apart runs connected in series by return bends in a sheet metal portion and superimposing the corrugated sheet portion upon another sheet metal portion with abonding material therebetween and with inserts of a material that will not bond to said sheet metal portions or to said bonding A material between and in contact with the sheet gation together, preventing surfaces of said aluportions and extending from one return bend to another adjacent return bend ofsaid corrugav tion, securing said inserts to one of said sheet metal portions, uniformly applying heat simultaneously over the entire exposed surfaces of the superimposed sheet portions to melt the bonding material and bond surfaces of the sheet metal portions around said inserts and said corrugation together whereby the surfaces of the sheet portions contacted by said inserts remain unbonded and the corrugation initially provides an open series flow passageway between the sheet metal portions, directing a cleaning fluid through said open series flow passageway to remove freign matter from the interior of the exchanger while preventing fluid ow from said one return bend to said another adjacent return bend at.

of the sheet portions at said inserts to form a. header interconnecting said corrugated return bends.

The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date Wellington Nov. 19, 1895 Number 10 Name Date Muiy Apr. 23, 1929 Johnson Nov. 8, 1932 Schweller Jan. 12, 1937 Hastings June 29, 1937 Mann Sept. 21, 1937 Raskin June 3. 1941 Money Dec. 23, 1941 Dalzell Dec. 29, 1942 McCullough Oct. 10, 1944 Furry Oct, 16, 1945 

